Font size for mobile calendar

You could make the calendar responsive by setting “Responsive maximum width” on the Options tab. This will switch to a list display on small screen.

If you really want to make the font smaller instead, you can use something like this:

@media screen and (max-width: 480px) {	
.spiffy {
    font-size: 10px;
}
}

You can adjust the weekday names using something like this:

.weekend-heading, .normal-day-heading {
    font-size: 10px;
}